I'm reversing the MobileMail.app, but seems like I can't find some symbols in all libraries, the _MFCreateStringWithData: is an example, I've even tried to find / -type f -exec grep -l _MFCreate {} \; on a 1.1.1's rootfs but found nothing.

Does anyone know where those _MF* methods are located?

Finally found it in MessageUI. The reason I didn't find it is because 'strings MessageUI | grep MFCreateStringWithData' didn't return anything, while a binary search 'grep MFCreateStringWithData MessageUI' did the magic. Besides, the classdump can't create the header files for these MF* methods.